The present invention relates to a liquid-crystal display apparatus including a liquid-crystal panel having a color filter and its light source and an electronic device, and particularly to a liquid-crystal display apparatus including a first light source for emitting light of white color (first white light) as a backlight and a second light source for emitting light of white color different from the first white color (second white light) such that the first and second light sources can be switched in response to ambient illuminance and an electronic device including the liquid-crystal display apparatus.
The Cited Patent Reference 1, for example, has so far described this kind of liquid-crystal display apparatus. That is, the Cited Patent Reference 1 has described a field sequential color liquid-crystal display apparatus suitable for displaying real pictures, such as a monitor receiver and a large-sized television receiver. The liquid-crystal display apparatus described in the Cited Patent Reference 1 includes a liquid-crystal panel, a light source for irradiating light to the liquid-crystal panel and a drive means for switching the color of the light source in a time-sequential fashion and which controls the state in which light is passed through or reflected on the liquid-crystal panel in synchronism therewith. This liquid-crystal display apparatus is characterized by a plurality of driving means composed of a driving means for carrying out color display by additive mixture of color stimuli from a time standpoint and a driving means for carrying out monochromatic color display by a single color based on gradation display.
According to the liquid-crystal display apparatus having the above-mentioned arrangement described in the Cited Patent Reference 1, since this liquid-crystal display apparatus has the arrangement in which the field sequential color system driving to carry out ordinary color display and the monochromatic color display driving without color cracking and of which power consumption is small are switched, there can be obtained the liquid-crystal display apparatus of which power consumption can be decreased on the whole and which is able to display real moving pictures with high definition.
The Cited Patent Reference 2 has described other example of a liquid-crystal display apparatus according to the related art. That is, the Cited Patent Reference 2 has described the liquid-crystal display apparatus using a liquid crystal as a display medium. The liquid-crystal display apparatus described in the Cited Patent Reference 2 includes a first transparent insulating substrate with a plurality of transparent pixel electrodes disposed thereon, a second transparent insulating substrate having transparent electrodes opposing to the above transparent pixel electrodes, a liquid crystal disposed between the above first and second transparent insulating substrates, a color display backlight light source disposed in an opposing fashion to the above second transparent insulating substrate to sequentially emit lights of colors of three primary colors and a control circuit for controlling the liquid crystal so as to properly orient molecules.
According to the liquid-crystal display apparatus having the above arrangement described in the Cited Patent Reference 2, since this liquid-crystal display apparatus has the arrangement in which lights of three primary colors of the color display backlight light source which emit lights of three primary colors are sequentially emitted and in which transmittance of one pixel is changed in response to each color, many colors can be expressed by one pixel and color display dot can be displayed by one pixel. Hence, resolution can be increased, a quantity of light can be prevented from being lost by the color filter, a quantity of light of the backlight light source can be used effectively and luminance of display can be increased.
[Cited Patent Reference 1]: Japanese Published Patent Application No. 2003-248463
[Cited Patent Reference 2]: Japanese Published Patent Application No. 6-110033
FIG. 1 of the accompanying drawings is a schematics diagram showing an example of a liquid-crystal display apparatus according to the related art. This liquid-crystal display apparatus according to the related art uses a light emitting diode for emitting light of white (W) as a light source of a backlight. A liquid-crystal display apparatus, generally depicted by reference numeral 1 in FIG. 1, is composed of a backlight 2, a first sheet polarizer 3, a first substrate 4, a liquid-crystal 5, a color filter 6, a second substrate 7 and a second sheet polarizer 8. The backlight 2 is composed of a plurality of white light-emitting diodes and these white light-emitting diodes are arrayed on the same straight line or on the same plane.
The first sheet polarizer 3 is bonded to one surface of the first substrate 4 and the backlight 2 is located behind the first sheet polarizer 3 with a proper gap in an opposing fashion. The liquid-crystal 5 is bonded to the other surface of the first substrate 4 and the color filter 6 is bonded to the other surface of the liquid-crystal 5. The color filter 6 has red (R), green (G) and B (blue) filter regions 6r, 6g and 6b repeatedly located thereon with the same gap in the upper and lower direction and in the right and left direction. Then, the second sheet polarizer 8 is bonded to the other surface of the second substrate 7.
Thus, when the backlight 2 is energized, emitted light of white color is irradiated from the first sheet polarizer 3 through the first substrate 4 to the liquid-crystal 5, and light that was passed through the liquid-crystal 5 is radiated to the outside from the second sheet polarizer 8 through the color filter 6 and the second substrate 7. In that case, light is passed through the filter regions 6r, 6g and 6b of the color filter 6, whereby lights of red (R), green (G) and blue (B) corresponding to the colors of the respective filter regions 6r, 6g and 6b are radiated to form a color image.
FIG. 2 is a schematic diagram showing another example of a liquid-crystal display apparatus according to the related art. This liquid-crystal display apparatus according to the related art uses more than three RGB light-emitting diodes to emit light of three colors of RGB of red, green and blue as a backlight light source thereof. A liquid-crystal display apparatus, generally depicted by reference numeral 10 in FIG. 2, has the arrangement identical to that of the liquid-crystal display apparatus 1 except a backlight 9. As shown in FIG. 2, the backlight 9 is composed of a combination of a red light-emitting diode to emit red, (R) light, a green light-emitting diode to emit green (G) light and a blue light-emitting diode to emit blue (B) light, and these three-color light-emitting diodes are repeatedly arrayed on the same plane at the same order.
Thus, when the backlight 9 is energized, emitted lights of three colors of red, green and blue colors are superimposed upon each other to generate light of white, and white light is irradiated from the first sheet polarizer 3 through the first substrate 4 to the liquid-crystal 5. Light that was passed through this liquid-crystal 5 is radiated to the outside from the second sheet polarizer 8 through the second substrate 7. In that case, light is passed through the filter regions 6r, 6g and 6b of the color filter 6, whereby lights of red, green and blue corresponding to the colors of the respective filter regions 6r, 6g and 6b are radiated to the outside to form a color image.
FIGS. 3A, 3B and 3C are respectively graphs graphing spectral characteristics of the aforementioned liquid-crystal display apparatus 1. Specifically, FIG. 3A is a graph showing spectral characteristics of the color filter 6, FIG. 3B is a graph showing spectral characteristics of the white light-emitting diode, and FIG. 3C is a graph showing spectral characteristics of the whole of the liquid-crystal display apparatus 1, respectively. As shown in FIG. 3A, in the spectral characteristics of the color filter 6, peaks of the spectral characteristics are generated at three portions. That is, the first peak corresponds to the blue filter region 6b and it has a peak value at a wavelength of approximately 470 nm as shown by a dot-and-dash line B. The second peak corresponds to the green filter region 6g and it has a peak value at a wavelength of approximately 520 nm as shown by a solid line G. Also, the third peak corresponds to the red filter region 6r and it has a peak value at a wavelength of approximately 620 nm as shown by a broken line R.
Further, as shown in FIG. 3B, in the white light-emitting diode, peaks of the spectral characteristics are generated at two portions. Specifically, the first peak lies at a wavelength of approximately 440 nm and the second peak lies in a wide range of wavelengths ranging of from approximately 530 nm to approximately 630 nm. The second peak is generated when three colors of red (R), green (G) and blue (B) are mixed. As a result, as shown in FIG. 3C, in the whole of the liquid-crystal display apparatus 1, peaks of the spectral characteristics are generated at three portions and large troughs are generated at two portions among the above-mentioned three peaks. The first trough is generated at a wavelength of approximately 480 nm and the second trough is generated at a wavelength of approximately 570 nm. These two troughs are generated when the three colors of R, G, B (red, greens, blue) are mixed.
FIGS. 4A, 4B and 4C are graphs graphing spectral characteristics of the aforementioned liquid-crystal display apparatus 10. More specifically, FIG. 4A is a graph showing spectral characteristics of the same color filter 6, FIG. 4B is a graph showing spectral characteristics of the RGB light emitting diodes, and FIG. 4C is a graph showing spectral characteristics of the whole of the liquid-crystal display apparatus 10, respectively.
As shown in FIG. 4A, in the RGB light-emitting diodes, peaks of the spectral characteristics are generated at three portions. Specifically, the first peak lies at wavelength of approximately 470 nm, the second peak lies at a wavelength of approximately 530 nm, and the third peak lies at a wavelength of approximately 630 nm. As shown in FIG. 4B, two troughs are generated among these three peaks. The first trough is generated at a wavelength of approximately 500 nm and the second trough is generated at a wavelength of approximately 580 nm. These two troughs are generated when the three colors of R, G, B (red, green, blue) are separated from each other.
Consequently, as shown in FIG. 4C, in the whole of the liquid-crystal display apparatus 10, peaks of the spectral characteristics are generated at three portions and large troughs are generated at the two portions among these three peaks. The first trough is generated at a wavelength of approximately 480 nm and the second trough is generated at a wavelength of 570 nm. These three peaks and two troughs correspond to the spectral characteristics of the RGB light-emitting diodes and they are generated when the three colors of R, G, B (red, green, blue) are separated from each other.
FIG. 5 is a graph showing color reproducing ranges of the liquid-crystal display apparatus 1 having the spectral characteristics shown in FIGS. 3A, 3B and 3C and the liquid-crystal display apparatus 10 having the spectral characteristics shown in FIGS. 4A, 4B and 4C. More specifically, a triangle 11, shown by a two-dot-and dash line in FIG. 5, shows a color reproducing range of the white light-emitting diode, and a triangle 12, shown by a solid line, shows a color reproducing range of the RGB three color light-emitting diodes. A study of the graph of FIG. 25 may reveal the fact that, when the RGB three light-emitting diodes are used as the backlight light source, the color reproducing ranges can be expanded in all regions of the red, green and blue regions as compared with the case in which the white light-emitting diode is used as the backlight light source.
In the above-mentioned liquid-crystal display apparatus, in recent years, various kinds of new technologies have been developed and adopted as methods for expanding the color reproducing range. For example, development or new pigments for use with color filters, improvements of LEDs of three colors and developments of new cold cathode-ray tubes are various kinds of new technologies.
In this case, most of electronic devices including a liquid-crystal display apparatus having a relatively large picture screen larger than a 10-inch-size picture screen, such as a large-sized liquid-crystal display panel type television receiver and a notebook size personal computer, use a cold cathode-ray tube (that is, cold CRT). However, since a high voltage is required to drive the cold cathode-ray tube, in the actual situations, the cold cathode-ray tube is hardly used in portable electronic devices because portable electronic devices tend to regard small power consumption as being important. Also, most of portable electronic devices such as a mobile phone with a small-size screen, a digital still camera, a built-in camera type image pickup apparatus and a PDA (personal digital assistant) uses a white LED (light-emitting diode), which can be driven by a low voltage, from various standpoints such as the size of electronic device products and power consumption.
However, while the liquid-crystal display apparatus described in the above-mentioned Cited Patent Reference 1 uses a black-and-white liquid-crystal display panel in which each pixel of the liquid-crystal panel is not provided with a color filter so that such liquid-crystal display apparatus is excellent in responsiveness of liquid-crystal, high-speed responsiveness being made possible, it is necessary to constantly switch the circuits by a switching unit in order to emit lights of red (R), green (G) and blue (B), and hence the related-art liquid-crystal display apparatus is not able to emit lights of red (R), green (G) and blue (B) at the same time. Therefore, because light-emissions of red (R), green (G) and blue (B) should be superimposed upon each other with a time lag, it is not possible to obtain a clear color of each pixel and hence a color reproducing capability of such related-art liquid-crystal display apparatus is not sufficient.
Also, in the liquid-crystal display apparatus described in the above-mentioned Cited Patent Reference 2, since three colors of the backlight light source which emits lights of three primary colors should be emitted sequentially, many colors are expressed at one pixel by changing transmittance of each color in one pixel in response to a pixel signal and one dot of color display is displayed by one pixel a clear color may not be obtained at each pixel and a color reproducing capability is not sufficient similarly as described above.
The problems that the present invention intends to solve are such ones in which the related-art liquid-crystal display apparatus should superimpose the light-emissions of red (R), green (G) and blue (B) upon each other with a time lag so that each pixel may not produce a clear color and that a color reproducing capability is not sufficient.